Infrared spectra of ultrastable zeolites derived from type Y zeolites

Abstract

An infrared spectroscopic study has been carried out on ultrastable zeolites derived from type Y zeolites and on their precursors. Both the hydroxyl stretching (3400 to 3800 cm −1) and the silica-alumina vibrational (300 to 1300 cm −1) regions of the spectra have been investigated. The effect of moisture content in the zeolite environment during calcination on the infrared spectrum of the zeolite has been established. An increase in moisture content at fixed calcination temperature results in additional absorption bands in the hydroxyl stretching region and in shifts to higher frequencies of absorption bands in the framework vibrational region, due primarily to dealumination of the zeolite framework. An increase in calcination temperature at fixed moisture content has a similar effect. Other effects observed are the suppression of dehydroxylation with increasing moisture content at temperatures up to 760 °C, and an increase in the degree of ordering of the zeolite structure under 100% steam at high temperatures. The last phenomenon is interpreted as being due to a structural rearrangement, involving silica migration into the vacancies created by the dealumination process. Pyridine adsorption experiments were done to determine the type of acid sites on ultrastable zeolites.